Multimedia Broadcasting Multicast Service (MBMS) is a technology designed to transmit data messages from a data source to multiple destination terminals in existing mobile packet communication network systems.
Presently, in legacy mobile communication network systems, Cell Broadcast Service (CBS) enables transmitting low bit rate data to all user terminals through shared broadcast channels in cells, and it belongs to a message service. Now, people's demand for mobile communication is no longer limited to telephone and message services. As Internet develops rapidly, a great deal of multimedia services come to the fore, and some application services require that multiple user terminals can receive identical data simultaneously, such as VOD, telecast, videoconference, online education, and interactive games, etc. Compared with general message services, those mobile multimedia data services are featured with high data volume, long duration, and high sensitivity to time delay, etc.
In order to utilize the resources in mobile communication networks more efficiently, 3GPP, the WCDMA/GSM Global Standardization Organization, has put forward MBMS. MBMS provides the PTM technology of transmitting data from a data source to multiple user terminals in mobile communication network systems and thereby implements sharing of network resources and improves utilization ratio of network resources, especially utilization ratio of air interface resource. MBMS supports not only broadcasting and multicasting of low data rate plain text messages but also broadcasting and multicasting of high data rate multimedia data services, which undoubtedly accommodates the developing trend to mobile data communication technology in the future.
When MBMS is based on a WCDMA/GSM mobile packet communication network, air interface resource can be shared through adding some new functional entities (e.g., Broadcasting Multicast—Service Center (BM-SC)) in the existing communications network system, adding MBMS capability in existing functional entities in PS-service domain, such as Service GPRS Supporting Nodes (SGSNs), Gateway GPRS Supporting Nodes (GGSNs), Radio Network Controllers (RNCs), and User Equipments (UEs), and defining new logically shared channels.
FIG. 1 shows a reference model of MBMS network implemented over GPRS packet mobile network in the prior art; wherein the BM-SC is a newly added MBMS functional entity mainly designed as an entry for the Content Provider and used to authorize and initiate MBMS bearer service in the mobile network, and transmit MBMS content to multiple UEs as scheduled. The edges of MBMS bearer service are Gmb and Gi reference points shown in the figure (i.e., the interface part between BM-SC and GGSN); wherein, Gmb interface is designed to provide functions on the control plane, while Gi interface is designed to provide bearer functions on the subscriber plane. In the network topology with MBMS capability shown in the figure, the only newly added interface is Gmb interface; other interfaces are existing ones in a WCDMA/GSM network system.
In the prior art, MBMS utilizes high speed radio transmission to send identical data created from the same data source to multiple mobile UEs; wherein, the sent data mainly comprises multimedia data required by Streaming service or Background QoS.
Wherein, each MBMS shall employ an appropriate bearer mode in each cell according to the number of subscribers of the MBMS: Point-to-Point (PTP) or Point-to-Multipoint (PTM) mode. Wherein, PTP bearer mode refers that the MBMS is borne on a dedicated channel of the subscriber who receives the MBMS, while PTM bearer mode refers that the MBMS is borne on a public channel in the mobile communication system.
In the prior art, the number of subscribers of a MBMS in a cell is counted through the Counting process. At present, in a mobile packet communication network system (e.g., GPRS network, 3G network, etc.), the Radio Network Controller (RNC) can wake up UEs in Idle mode and perform counting such UEs in certain conditions.
Wherein, in the RNC in a network system, a corresponding MBMS Service Context is configured for each MBMS. Each MBMS Service Context contains the records of UEs that are added to the MBMS and in RRC Connected or PMM-Connected Mode. Through performing counting the number of UEs recorded in each MBMS Service Context, RNC can obtain the number of subscribers who receive a MBMS in a cell and choose the corresponding bearer mode according to the number of subscribers of each MBMS in each cell, so as to transmit corresponding MBMS service data to multiple UEs.
At present, in the TS25.346 Protocol issued by 3GPP, counting the number of subscribers of each MBMS in each cell is stipulated as follows:
If the Radio Resource Management (RRM) in the network system requires counting the number of subscribers of each MBMS in each cell, the following steps have to be executed:
1) A MBMS session is initiated;
2) RNC converts subscribers in URA_PCH (UTRAN Registration Area Public Channel) state to as in CELL_PCH (CELL Public Channel) state through paging (wherein, URA_PCH and CELL_PCH are two working states of UEs under control of RNC in a 3G network system);
3) RNC pages UEs in Idle mode with Terminal Mobile Group Identify (TMGI), so that the UEs establish Radio Resource Connected (RRC) connections to RNC; then, RNC obtains the information of each existing subscriber receiving the MBMS service data in each cell through the Core Network (CN), and records the subscriber information into the MBMS Service Context corresponding to the MBMS;
4) RNC performs counting the number of subscribers recorded in the MBMS Service Context corresponding to the MBMS; if RNC finds the number of subscribers receiving the MBMS service data exceeds a predefined threshold (the threshold for switching between PTP and PTM mode), RNC will transmit the MBMS service data to multiple UEs in PTM mode in the cell, i.e., it will transmit the MBMS service data to multiple UEs through public channel broadcasting;
if RNC finds the number of subscribers is less than the predefined threshold, RNC will transmit the MBMS service data to UEs requiring the MBMS service data in PTP mode in the cell, i.e., it establishes a dedicated channel to each subscriber and transmits the MBMS service data to the subscriber;
5) in the above transmission process of MBMS service data, RNC can also perform Recounting operation.
However, the method of performing counting the number of subscribers of each MBMS in each cell with above technology has the following drawbacks:
(A) In step 3), subscribers in CELL-PCH state and subscribers in URA-PCH state may not be distinguished clearly from each other in the counting processes in different cases; therefore, the counting may be incomplete and thus may cause an inaccurate result during RNC performing counting the number of subscribers of a MBMS, and thereby RNC may send MBMS service data to UEs which need not receive the MBMS service data, resulting in waste of air interface resource.
(B) In the above process of counting the number of subscribers of a MBMS, for each subscriber who has subscribed a MBMS and is in CELL_DCH state or CELL_FACH state, RNC deems the UE will receive the MBMS service data by default. Actually, the UE may not intend to receive the MBMS service data. However, RNC will count such UEs in the Counting, resulting in error in the counting result and in waste of air interface resource as well.